Hyaluronic acid is a mucopolysaccharide which exists in a living body (particularly subcutaneous tissue). Hyaluronic acid or its salt has been widely used as a raw material for cosmetics due to high moisture retention properties. It has been confirmed that oral administration of hyaluronic acid or its salt compensates for a decrease in hyaluronic acid content of a living body to improve moisture retention, elasticity, and flexibility of the skin. Therefore, hyaluronic acid and its salt are added to various types of food.
However, hyaluronic acid is a polysaccharide having an extremely high molecular weight and a high viscosity. Therefore, when hyaluronic acid is added in an amount exceeding a specific amount, preparation may become difficult due to high viscosity, or the viscosity of the resulting cosmetics or food may be affected, whereby the feel during use may deteriorate or the texture may be impaired.
In order to reduce the viscosity of hyaluronic acid while maintaining its functions, a method has been developed which reduces the molecular weight of the hyaluronic acid (JP-A-63-57602). This application discloses a method of decomposing hyaluronic acid by treatment with an alkali or an acid to reduce the molecular weight of the hyaluronic acid. However, since this method requires that the alkali or acid treatment conditions be made severe in order to reduce the molecular weight, it is difficult to obtain a low-molecular-weight hyaluronic acid. According to this method, hyaluronic acid browns under strongly acidic or strongly basic conditions. Since brown hyaluronic acid is not suitable as a raw material for cosmetics or food, purification for decolorization may be necessary, or it may be difficult to decolorize the hyaluronic acid by purification to such an extent that the hyaluronic acid can be used as the raw material for cosmetics or food.